The basic circuit of a pseudo random pattern generator (hereinafter referred to simply as a RP generator as well) is made up of a shift register and at least one XOR (an exclusive OR circuit). FIG. 4 is a diagrammatic showing of its example, in which a generator polynomial (or generating function) is expressed by F(X) =X.sup.5 +X.sup.2 +1 and five D-FF (D type flip-flop) stages and one XOR are employed. As shown, for the generation of a pseudo random pattern (PRBS: Pseudo Random Binary Sequence) a feedback type shift register is used and, for example, the outputs from its final stage and any one of its intermediate stages are input into the XOR, whose output is fed back to the input of the shift register. Upon each input of one clock pulse (CK) into this circuit, PRBS data of one or more bits is produced from an arbitrary one or more shift stages.
As is well-known in the art, the pseudo random pattern generator having an n-order generator polynomial F(X) is usually formed by an n-stage shift register type circuit and PRBS data from each shift stage is a repetition of a pattern of successive 2.sup.n -1 bits. The outputs from any shift stages have patterns of the same sequence and they are displaced apart in phase alone. Hence, the output from any shift stage may be used as the PRBS data from the pseudo random pattern generator. It is also possible to use outputs from an arbitrary number of shift stages as random pattern data.
As depicted in FIG. 5, a conventional m-channel pseudo random pattern generating device is comprised of RP generators 1.sub.1 through 1.sub.m that have different generator polynomials F.sub.1 (X), F.sub.2 (X), ..., F.sub.m (X), respectively. Since the generator polynomials F.sub.i (X) (where i=1 through m) differ from one another, cross-correlation of the PRBS data in the respective channels CH.sub.i can be made low.
There is the possibility that as the number m of channels used increases (more than 100, for instance), conventional multi-channel PRBS generating devices could not be implemented because the number of existing generator polynomials F.sub.i (X) is about 100. Moreover, the RP generator in each channel is formed on the basis of a different generator polynomial, and hence has a different circuit configuration accordingly; thus, it is impossible to standardize the circuit configuration of the RP generators in the respective channels and difficult to fabricate them as IC's.